Capacitance measurement of high voltage device

ABSTRACT

Described herein are systems and methods that facilitate the measurement of the capacitance of high voltage devices while shielding an active device involved in the measurement from the high voltage. The systems and methods employ capacitors to store the high voltage such that the active device does not experience the high voltage. Placement of a reset device ensures that the active device is shielded from the high voltage.

TECHNICAL FIELD

This disclosure generally relates to measurement of the capacitance of ahigh voltage device and more specifically relates measurement of thecapacitance of a high voltage device without exposing active deviceinvolved in the measurement to the high voltage of the high voltagedevice.

BACKGROUND

An active device utilized integrated in the measurement of capacitanceof a device is often limited with regard to the voltage it can beexposed to while conducting the measurement. The voltage limit can bedue to a terminal or breakdown voltage that prevents the active devicefrom receiving any voltages above the breakdown voltage without leakingsignificant current and dramatically reducing the life of the activedevice. Usual breakdown voltages in modern technologies can be in therange of 1 V to 10 V.

A high voltage device is generally a device that can operate under avoltage greater than the breakdown voltage of the active device. Acapacitive microelectromechanical system (MEMS) device is an example ofsuch a high voltage device. A capactive MEMS device facilitates themovement of elements by an applied voltage. The amount of movement doesaffect the capacitance of the capacitive MEMS device. Measurement of thecapacitance of the capacitive MEMS device is difficult with atraditional capacitive measurement circuit circuit because the voltagerequired to move the elements a certain amount is often greater than thebreakdown voltage of the active device of the traditional capacitivemeasurement circuit.

Traditional capacitance measurements are performed by connecting thehigh voltage device to a circuit, including the active device. However,this connection can significantly limit the voltage that can be appliedto the high voltage device or can significantly limit the sensitivity ofthe circuit that facilitates the measurement. In fact, when the voltageapplied to the device is higher than the breakdown voltage of the activedevice (as in the case of capacitive MEMS devices), the measurement ofthe capacitance of the high voltage device becomes impossible.

SUMMARY

The following presents a simplified summary to provide a basicunderstanding of some aspects of the subject disclosure. This summary isnot an extensive overview of the disclosed subject matter. It is notintended to identify key or critical elements of the disclosed subjectmatter, nor is it intended to delineate the scope of the subjectdisclosure or the claims. Its sole purpose is to present some conceptsof the disclosed subject matter in a simplified form as a prelude to themore detailed description presented later.

In a non-limiting embodiment of the subject disclosure, a system isdescribed that facilitates the isolation of a high voltage that isapplied to an external device (e.g., a high voltage external device likea capacitive MEMS device) in capacitance measurement. The systemincludes an amplifier with a positive input, a negative input, and anoutput and two capacitors that each store a high voltage. The firstcapacitor is connected to the negative input of the amplifier and to anexternal device with an unknown capacitance. The second capacitor isconnected to the output of the amplifier and to the external device. Thesystem also includes a voltage source device that supplies a low voltageto the positive input of the amplifier and a reset device that connectsthe output of the amplifier and the negative input of the amplifier. Adetector device can measure a change in the output voltage of theamplifier as a function of a change in the low voltage supplied by thevoltage source and function of the unknown capacitance of the externaldevice.

In another non-limiting embodiment of the subject disclosure, a methodis described that facilitates measurement of capacitance of an externaldevice, even when the external device is exposed to a high voltage. Themethod includes storing a high voltage on the external device with anunknown capacitance, on a first capacitor between a negative input of anamplifier and the external device, and on a second capacitor connectedbetween the output of the amplifier and the external device. A lowvoltage is then applied to a positive input of the amplifier. Thevoltage of the output of the amplifier and a voltage of the negativeinput of the amplifier are driven to the same low voltage via a resetdevice. The low voltage applied at the positive input of the amplifiercan be modified, and the voltage change out of output of the amplifiercan be measured. The voltage change at the output of the amplifier isproportional to the unknown capacitance and to the voltage changeapplied at the positive input of the amplifier.

In a further non-limiting embodiment of the subject disclosure, acapacitance measuring circuit is described. The capacitance measurementcircuit is operational to measure the capacitance of an external device,even when the external device is exposed to a high voltage. Thecapacitance measuring circuit includes an amplifier that includes apositive input, a negative input, and an output, a first capacitor thatstores a high voltage connected to the negative input of the amplifierand to the external device with an unknown capacitance, a secondcapacitor that stores the high voltage connected to the output of theamplifier and to the external device. The capacitance measuring circuitalso includes a reset device that connects the output of the amplifierand the negative input of the amplifier and facilitates driving theoutput of the amplifier and the negative input of the amplifier to a lowvoltage supplied by a voltage source device to the positive input of theamplifier. Accordingly, a change in the output voltage of the amplifieras a result of a change of voltage supplied by the voltage source is afunction of the unknown capacitance of the external device.

The following description and the annexed drawings set forth in detailcertain illustrative aspects of the disclosed subject matter. Theseaspects are indicative, however, of a few of the various ways in whichthe principles of the innovation may be employed. The disclosed subjectmatter is intended to include all such aspects and their equivalents.Other advantages and distinctive features of the disclosed subjectmatter will become apparent from the following detailed description ofthe innovation when considered in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Non-limiting and non-exhaustive embodiments of the subject disclosureare described with reference to the following figures, wherein likereference numerals refer to like parts throughout the various viewsunless otherwise specified.

FIG. 1 is a schematic illustration of an example system that facilitatesmeasurement of capacitance of an external device, according to anembodiment of the subject disclosure;

FIGS. 2-4 are schematic illustrations of the system that facilitatesmeasurement of capacitance of an external device with different types ofreset devices, according to an embodiment of the subject disclosure;

FIG. 5 is a schematic illustration of an example of a more detailedsystem that facilitates measurement of capacitance of an externaldevice, according to an embodiment of the subject disclosure;

FIG. 6-8 are schematic illustrations of the more detailed system thatfacilitates measurement of capacitance of an external device withdifferent types of connecting devices, according to an embodiment of thesubject disclosure;

FIG. 9 is a schematic illustration of another example system thatfacilitates measurement of capacitance of an external device, accordingto an embodiment of the subject disclosure;

FIG. 10 is a schematic illustration of a further example system thatfacilitates measurement of capacitance of an external device, accordingto an embodiment of the subject disclosure;

FIG. 11 is a process flow diagram of a method that facilitatesmeasurement of capacitance of an external device, according to anembodiment of the subject disclosure;

FIG. 12 is a process flow diagram of a more detailed method that furtherfacilitates measurement of capacitance of an external device, accordingto an embodiment of the subject disclosure;

FIG. 13 is an example integrated circuit that can facilitateapplications of the systems and methods according to the embodimentsdescribed in the subject disclosure; and

FIG. 14 is an example configuration of components within an integratedcircuit that facilitate the applications of the systems and methodsaccording to the embodiments described in the subject disclosure.

DETAILED DESCRIPTION

In the following description, numerous specific details are set forth toprovide a thorough understanding of the embodiments of the subjectdisclosure. One skilled in the relevant art will recognize, however,that the embodiments described herein can be practiced without one ormore of the specific details, or with other methods, components,materials, etc. In other instances, well-known structures, materials, oroperations are not shown or described in detail to avoid obscuringcertain aspects.

Described herein are systems and methods that facilitate the measurementof the capacitance of an external voltage device that operates under ahigh voltage (high voltage device) while shielding an active deviceinvolved in the measurement of the capacitance from the high voltage.The systems and methods can, for example, be utilized in the measurementof the capacitance of a high voltage device that operates with a voltagehigher than the breakdown voltage of the active device involved in themeasurement. The voltage of applied to the high voltage device is notlimited based on the breakdown voltage of the active device.Accordingly, the systems and methods can avoid a loss of precision inthe measurement principle, while avoiding extra electrodes ordifferential measurement system, thereby reducing costs and reducingsize.

Referring now to FIG. 1, illustrated is a schematic illustration of anexample system 100 that facilitates measurement of capacitance of anexternal device 106, according to an embodiment of the subjectdisclosure, where the capacitance of the external device 106 is unknownand the external device 106 is a high voltage device. System 100facilitates determination (or measurement) of the capacitance byshielding the active elements that facilitate the capacitancemeasurement (e.g., amplifier 102; other examples of active devicesinclude transistors and other integrated circuit elements) from the highvoltage of the external device 106 that is outside the inherent voltagelimitations of the active device.

In an embodiment, the external device 106 is a high voltage device thatoperates at a voltage higher than the inherent voltage limitations of anactive device that facilitates the measurement of the capacitance. Theinherent voltage limit of the active device can be a breakdown voltage.For example, the high voltage is greater than the breakdown voltage ofthe active device. A voltage greater than the breakdown voltage resultsin failure of the active device, leakage of current and reduction of thelife of the active element. In modern technologies the breakdown voltagecan be in the range of 1 V to 10 V, and the high voltage is greater thana voltage in the range of 1 V to 10 V.

One example of a high voltage device is a capacitive MEMS device.Generally, a high voltage is applied to a capacitive MEMS device suchthat elements of the capacitive MEMS device can be moved correspondingto the voltage. The positions of the elements can be determinedaccording to the capacitance of the MEMS.

To isolate the active device (amplifier 102) from the high voltage,system 100 employs two capacitors 104 and 108 to store the high voltageof the external device 106 without letting the active device (amplifier102) experience the high voltage. System 100 is different from a systemthat only uses a used a simple capacitive divider to facilitatemeasurement of the capacitance of the external device 106. A simplecapacitive divider would ensure that the capacitance value detected bythe detector device 114 would be divided by the ratio of the capacitors,which reduces the sensitivity of the acquisition circuit and provides astrongly non-linear reading. Instead, system 100 also utilizes anamplifier 102 (e.g., an operational amplifier) to facilitate measurementof the capacitance of the external device 106 in a more linear, highersensitivity manner.

The amplifier 102 is an active device that operates under a low voltage,so the capacitors 104 and 108 shield the amplifier 102 from the highvoltage of the external device 106. Since the amplifier 102 is shieldedfrom the high voltage of the external device 106, the amplifier only isexposed to a low voltage applied by voltage source 110. Accordingly, theexternal device 106 can still operate at a high voltage without system100 requiring a special high voltage precision device that would limitthe choice of the technology, reduce precision, and increase productioncosts to sense the capacitance of the external device 106.

The amplifier 102 of system 100 has a positive input (+), a negativeinput (−) and an output. A capacitor 104 (or “first capacitor”) isconnected to the negative input (−) of the amplifier 102 and to theexternal device 106. A capacitor 108 (or “second capacitor”) isconnected to the output of the amplifier and to the external device 106.The first capacitor 104 and the second capacitor 108 store the highvoltage applied to the external device 106 to shield the amplifier 102and the detector device 114 from the high voltage. The “high voltage”refers to any voltage greater than the voltage applied during themeasurement of the capacitance of the external device with system 100.Generally the high voltage is greater than the breakdown voltage of anactive device.

To provide context for the “high voltage,” several examples areprovided. However, these examples are not meant to limit system 100 toapplications with these particular voltages. It will be understood thatthe high voltage can be any voltage higher than a voltage limitation ofan active device (e.g., amplifier 102). For example, in an embodiment,the high voltage is at least about eight Volts. In another embodiment,the high voltage is at least about nine Volts. In a further embodiment,the high voltage is at least about ten Volts.

The system 100 also includes a voltage source device 110. The voltagesource device 110 supplies a low voltage to the positive input (+) ofthe amplifier 102. The low voltage does affect the output voltage of theamplifier 102 or the input voltage of the detector device 114. The “lowvoltage” can refer generally to any voltage less than the “highvoltage.” In other words, the low voltage can refer to any voltage lessthan the breakdown voltage of an active device in an integrated circuit.

To provide context for the “low voltage,” several examples are provided.However, these examples are not meant to limit system 100 toapplications with these particular voltages. It will be understood thatthe low voltage can be any voltage within the voltage limitations of anactive device (e.g., amplifier 102). For example, in an embodiment, thelow voltage is about five Volts or less. In another embodiment, the lowvoltage is about four Volts or less. In a further embodiment, the lowvoltage is about three Volts or less.

The low voltage is applied by the voltage source device 110 to thepositive input (+) of the amplifier 102. The voltage (Vo) of the outputof the amplifier 102 and the voltage of the negative input (−) of theamplifier 102 are driven to the same low voltage via a reset device 112.The reset device 112 connects the output of the amplifier 102 and thenegative (−) input of the amplifier 102.

The reset device 112 can be any device that can provide both a lowimpedance that facilitates current flow and a high impedance thatimpedes or prevents current flow. Non-limiting examples of the resetdevice 112 are shown in FIG. 2-4.

FIGS. 2-4 are schematic illustrations of example configurations of thesystem 200, 300, 400 that facilitates measurement of capacitance of anexternal device 106 with different reset devices 202, 302, 402. FIG. 2shows a switch 202 being used as the rest device. FIG. 3 shows aresistor 302 being used as the reset device. FIG. 4 shows an inductor402 being used as the reset device.

Referring back to FIG. 1, the detector device 114 of system 100 candetermine, measure, detect, or the like, the capacitance of the externaldevice 106. Detector device 114 is not exposed to the high voltage ofthe external device 106. The detector device 114 can be any device thatcan facilitate determination, measurement, detection, or the like, ofthe capacitance of the external device 106. In an embodiment, thedetector device 114 can include an analog to digital convertor.

To facilitate determination of the capacitance, the low voltage appliedat the positive input (+) of the amplifier 102 by the voltage sourcedevice 110 when the reset device 112 is at high impedance. For example,the voltage can be modified as a step or pulse. At the moment of thestep or pulse, the voltage of the output (Vo) of the amplifier 102represents the unknown capacitance of external device 106.

The detector device 114 measures a change in the output voltage of theamplifier 102 as a function of a change in the low voltage supplied bythe voltage source and the unknown capacitance of the external device.The change in the output voltage of the amplifier 102 can also be afunction of the capacitance of the second capacitor 108.

The range of the determination can be affected by several factors. Theprecision can be improved by setting the step or pulse to be small(e.g., having a small voltage difference from the original voltagesupplied by the power source 110). The range can also be improved bysetting the ratio of the unknown capacitance to the capacitance of thesecond capacitor 108 as large.

Referring now to FIG. 5, illustrated is a schematic illustration of anexample system 500 that facilitates application of the high voltage tothe external device 106, according to an embodiment of the subjectdisclosure. System 500 employs the two capacitors 104, 108, theamplifier 102, the voltage source 110, the reset device 112, theexternal device 106 and the detector device 114 as described above withrespect to FIG. 1. System 500 additionally provides a mechanism forapplying the high voltage to the external device 106. The high voltagecan be stored by the two capacitors 104 and 108 to shield the rest ofthe system 500 (e.g., any active devices) from the high voltage.

System 500 illustrates a voltage gain device 502 that can generate thehigh voltage of the external device 106. The voltage gain device 502 caninclude, for example, a booster or a charge pump. System 500 alsoincludes a connecting device 504 that connects the voltage gain device502 to the external device 106 and the capacitors 104 and 108. Thecapacitors 104 and 108 isolate the rest of system 500 (e.g., theamplifier 102, which is an active device) from the high voltage of thevoltage gain device 502. This allows the high voltage to be managedusing regular modern technology with no extra costs related to specialfeatures like high voltage precision analog devices, so the circuitry ofsystem 500 can remain highly integrated.

The connecting device 504 can be any device that can provide both a lowimpedance that facilitates current flow and a high impedance thatimpedes or prevents current flow. Non-limiting examples of theconnecting device 504 are shown in FIG. 6-8.

FIGS. 6-8 are schematic illustrations of example configurations of thesystem 600, 700, 800 that facilitates establishing the high voltage ofthe external device 106 with different connecting devices 602, 702, 802.FIG. 6 shows a switch 602 being used as the connecting device. FIG. 7shows a resistor 702 being used as the connecting device. FIG. 8 showsan inductor 802 being used as the connecting device. It will beunderstood that the reset device 112 as shown in FIGS. 6-8 need not bethe same variable impedance device as the connecting device 504.Moreover, the reset device can be any device that facilities transitionbetween low impedance and high impedance, including those devices shownin FIG. 2-4.

Referring back to FIG. 5, when the reset device 112 and the connectingdevice 504 are at low impedance, the external device 106 receives thehigh voltage. The high voltage is also stored on the capacitors 104 and106. During this time, since the reset device 112 provides lowimpedance, the voltage of the negative input is kept at the same voltageas the output (Vo) of the amplifier 102. The voltage of the output (Vo)is equal to the low voltage supplied by the voltage generator 110.

When the reset device 112 and the connecting device 504 are at highimpedance, the voltage source 110 modifies the low voltage (e.g., via apulse or step) to the positive input (+) of the amplifier. The modifiedvoltage can be represented with respect to the low voltage as a changeof Vd.

The output voltage of the amplifier 102 changes to force the voltage ofnegative input (−) of amplifier 102 to match the voltage of the positiveinput (+) of the amplifier (a change of Vd). Since the negative input(−) of the amplifier 102 is connected to the external device 106 throughthe first capacitor 104, the voltage of the external device 106 mustalso change by the same value (a change of Vd). For the voltage of theexternal device 106 to change by a value of Vd, the output voltage Vomust change by a voltage of (the capacitance of the external device 106divided by the capacitance of the second capacitor 108)*Vd. Accordingly,the change in the output voltage (Vd) is a measure of the capacitance ofthe external device 106.

During the whole process, no active device is exposed to a high voltage.In other words, the voltages of the positive input (+) of the amplifier102, the negative input (−) of the amplifier 102 and the output of theamplifier 102 remain at low voltages. The external device 106 andcapacitors 104 and 108 see the high voltage supplied by the voltage gaindevice 502. The connector device 504, the reset device 112 and theoutput stage of the voltage gain device can be less precise (e.g., madeof high voltage transistors or other components designed to support thehigh voltage). Additionally, by selecting the voltage difference Vdsmall and the ratio of the unknown capacitance of the external device106 to the capacitance of the second capacitor 108 large, the value thecapacitance fo the external device 106 can be determined over a widerange without generating an large voltage change on the external device106 while the capacitance of the external device 106 is determined.

Referring now to FIGS. 9 and 10, illustrated are alternateconfigurations that can be used in place of system 100. Theseconfigurations are merely examples and are not meant to be excusive.FIGS. 9 and 10 are meant to represent any configuration that limits oreliminates the potential change at the negative input (−) of theamplifier 102. Moreover, it will be understood that any configurationutilizing at least two capacitors to isolate active elements from highvoltage are meant to fall under the scope of this disclosure, evenconfigurations that do not limit or eliminate the potential change atthe input of the amplifier 102.

FIG. 9 illustrates an amplifier 102 with the voltage source 102 and acapacitor 902 (the “third capacitor”) at the negative input (−).Accordingly, the voltage source device is not connected to the positiveinput (+) of the amplifier 102, but to a third capacitor 902 connectedbetween the voltage source 110 and the negative input (−) of theamplifier 102. The positive input (+) of the amplifier 102 is connectedto ground.

FIG. 10 illustrates the amplifier 102 with the voltage source 110 and acapacitor 902 at the negative input (−) of the amplifier 102 and avoltage driver 1002 at the positive input (+) of the amplifier 102.Accordingly, the voltage source device is not connected to the positiveinput (+) of the amplifier 102, but to a third capacitor 902 connectedbetween the voltage source and the negative input (−) of the amplifier102. The positive input (+) of the amplifier 102 is connected to voltagedriver 1002 that can provide a fixed bias voltage.

Further alternate configurations are possible that utilize differentactive devices than the amplifier 102 shown in FIGS. 1-10. An example ofan alternate active device is a transistor. The configuration of the twocapacitors 104 and 108 will change in a manner that will protect thetransistor from the high voltage.

FIGS. 11 and 12 show methods illustrated as flow diagrams 1100 and 1200.For simplicity of explanation, the methods are depicted and described asseries of acts. However, the methods are not limited by the actsillustrated and by the order of acts. For example, acts can occur invarious orders and/or concurrently, and with other acts not presentedand described herein. Furthermore, not all illustrated acts may berequired to implement the methods. Additionally, it should be furtherappreciated that the methods can be implemented on an article ofmanufacture (e.g., within a circuit, such as an integrated circuit) tofacilitate transporting and transferring the methods.

Referring now to FIG. 11, illustrated is a process flow diagram of amethod 1100 that facilitates measurement of an unknown capacitance of ahigh voltage external device, according to an embodiment of the subjectdisclosure. The external device can be a high voltage device thatoperates at a higher voltage than the breakdown voltage of an activedevice within an integrated circuit (e.g., a capacitive MEMS device).Method 1100 can facilitate the measurement of the unknown capacitance ofthe external device while shielding the integrated circuitry of themeasurement device from the high voltage without limiting the highvoltage applied to the external device.

At element 1102, a high voltage is applied to the external devicewithout reaching any active devices of the capacitance measurementcircuit. This is due to two capacitors placed between the externaldevice and the active devices of the capacitance measurement device thatstore the high voltage without letting the high voltage reach the activedevices. In an example, the active device can be an amplifier. In thiscase, the two capacitors include a first capacitor connected between anegative input an amplifier and the external device and a secondcapacitor connected between the output of the amplifier and the externaldevice. The high voltage is stored on an external device, the firstcapacitor and the second capacitor such that the amplifier does not seethe high voltage of the external device. Accordingly, the externaldevice can still operate at a high voltage without the capacitivesensing device requiring a special high voltage precision device thatwould limit the choice of the technology, reduce precision, and increaseproduction costs to sense the capacitance of the external device.

The “high voltage” refers to any voltage greater than the voltageapplied during the measurement of the capacitance of the external devicewith system 100. Generally the high voltage is greater than thebreakdown voltage of an active device. To provide context for the “highvoltage,” several examples are provided. However, these examples are notmeant to limit system 100 to applications with these particularvoltages. For example, in an embodiment, the high voltage is at leastabout eight Volts. In another embodiment, the high voltage is at leastabout nine Volts. In a further embodiment, the high voltage is at leastabout ten Volts.

At element 1104, a low voltage is applied to a positive input of theamplifier. The low voltage is generally a voltage that does not affectthe sensitivity of the active device, such as the amplifier. The “lowvoltage” can refer generally to any voltage less than the “highvoltage.” In other words, the low voltage can refer to any voltage lessthan the breakdown voltage of an active device in an integrated circuit.

To provide context for the “low voltage,” several examples are provided.However, these examples are not meant to limit system 100 toapplications with these particular voltages. For example, in anembodiment, the low voltage is about five Volts or less. In anotherembodiment, the low voltage is about four Volts or less. In a furtherembodiment, the low voltage is about three Volts or less.

At element 1106, a voltage of the output of the amplifier and thevoltage of the negative input of the amplifier are driven to the samelow voltage via a reset device. The reset device connects the output ofthe amplifier and the negative input of the amplifier. The reset devicecan be any device that can provide both a low impedance that facilitatescurrent flow and a high impedance that impedes or prevents current flow.Non-limiting examples of the reset device include a resistor, a switchand an inductor.

At element 1108, the low voltage is modified at the positive input ofthe amplifier. The modification can be accomplished by the voltagesource when the reset device is at high impedance. For example, thevoltage can be modified as a step or pulse. At the moment of the step orpulse, the voltage of the output of the amplifier represents the unknowncapacitance of external device. Accordingly, at element 1110, a voltagechange of the output of the amplifier is measured that is proportionalto the unknown capacitance and to the voltage change applied at thepositive input of the amplifier. The change in the output voltage of theamplifier can also be a function of the capacitance of the secondcapacitor.

The precision of the determination can be affected by several factors.The precision can be improved by setting the step or pulse to be small(e.g., having a small voltage difference from the original voltagesupplied by the voltage source). The precision can also be improved bysetting the ratio of the unknown capacitance to the capacitance of thesecond capacitor as large.

Referring now to FIG. 12, illustrated is a process flow diagram of amethod 1200 that further facilitates measurement of capacitance of anexternal device, according to an embodiment of the subject disclosure.Like method 1100, method 1200 can facilitate the measurement of theunknown capacitance of the external device while shielding theintegrated circuitry of the measurement device from the high voltagewithout limiting the high voltage applied to the external device. Theexternal device can be a high voltage device that operates at a highervoltage than the breakdown voltage of an active device within anintegrated circuit (e.g., a capacitive MEMS device).

At element 1202, a high voltage is applied to the external devicewithout reaching any active devices of the capacitance measurementcircuit. This is due to two capacitors placed between the externaldevice and the active devices of the capacitance measurement device thatstore the high voltage without letting the high voltage reach the activedevices. In an example, the active device can be an amplifier. In thiscase, the two capacitors include a first capacitor connected between anegative input an amplifier and the external device and a secondcapacitor connected between the output of the amplifier and the externaldevice. The high voltage is stored on an external device, the firstcapacitor and the second capacitor such that the amplifier does not seethe high voltage of the external device. Accordingly, the externaldevice can still operate at a high voltage without the capacitivesensing device requiring a special high voltage precision device thatwould limit the choice of the technology, reduce precision, and increaseproduction costs to sense the capacitance of the external device.

The “high voltage” refers to any voltage greater than the voltageapplied during the measurement of the capacitance of the external devicewith system 100. Generally the high voltage is greater than thebreakdown voltage of an active device. To provide context for the “highvoltage,” several examples are provided. However, these examples are notmeant to limit system 100 to applications with these particularvoltages. For example, in an embodiment, the high voltage is at leastabout eight Volts. In another embodiment, the high voltage is at leastabout nine Volts. In a further embodiment, the high voltage is at leastabout ten Volts.

The high voltage can be supplied by a voltage gain device. The voltagegain device can be any device that can generate the high voltagerequired by the external device for operation. The voltage gain devicecan include, for example, a booster or a charge pump.

The voltage gain device can be connected to the external device and thecapacitors through a connecting device. The connecting device can be anydevice that can provide both a low impedance that facilitates currentflow and a high impedance that impedes or prevents current flow. Forexample, the connecting device can be a switch, a resistor or aninductor.

The capacitors isolate active devices used for measurement (e.g.,measurement of the capacitance of the external device) from the highvoltage of the voltage gain device. This allows the high voltage to bemanaged using regular modern technology with no extra costs related tospecial features like high voltage precision analog devices, so thecircuitry of the measurement system can remain highly integrated.

At element 1204, a low voltage is applied to a positive input of theamplifier. The low voltage is generally a voltage that does not affectthe sensitivity of the active device, such as the amplifier. The “lowvoltage” can refer generally to any voltage less than the “highvoltage.” In other words, the low voltage can refer to any voltage lessthan the breakdown voltage of an active device in an integrated circuit.

To provide context for the “low voltage,” several examples are provided.However, these examples are not meant to limit system 100 toapplications with these particular voltages. For example, in anembodiment, the low voltage is about five Volts or less. In anotherembodiment, the low voltage is about four Volts or less. In a furtherembodiment, the low voltage is about three Volts or less.

At element 1206, a voltage of the output of the amplifier and thevoltage of the negative input of the amplifier are driven to the samelow voltage via a reset device. The reset device connects the output ofthe amplifier and the negative input of the amplifier. The reset devicecan be any device that can provide both a low impedance that facilitatescurrent flow and a high impedance that impedes or prevents current flow.Non-limiting examples of the reset device include a resistor, a switchand an inductor.

When the rest device and the connecting device are at low impedance, theexternal device receives the high voltage and the high voltage is storedon the capacitors. During this time, since the rest device provides lowimpedance, the voltage of the negative input is kept at the same voltageas the output of the amplifier, which is equal to the low voltagesupplied by the voltage generator.

At element 1208, an impedance of the reset device between the negativeinput of the amplifier and the output of the amplifier is increased. Atelement 1210, an impedance of the connecting device between a voltagegain device and the external device is increased. With the reset deviceand the connecting device each at high impedance, at element 1212, thelow voltage is modified at the positive input of the amplifier (e.g., bythe voltage source).

The output voltage of the amplifier changes to force the voltage of thenegative input of the amplifier to match the voltage of the positiveinput of the amplifier. Since the negative input of the amplifier isconnected to the external device through the first capacitor, thevoltage of the external device must also change by the same value. Forthe voltage of the external device to change by the same value as thechange in the output voltage, the output voltage must change by avoltage of (the capacitance of the external device divided by thecapacitance of the second capacitor) multiplied by the value of thevoltage change.

At element 1214, the voltage change of the output of the amplifier ismeasured that is proportional to the unknown capacitance and to thevoltage change applied at the positive input of the amplifier.Accordingly, the change in the output voltage is a measure of thecapacitance of the external device.

During the whole process, no active device is exposed to a high voltage.In other words, the voltages of the positive input of the amplifier, thenegative input of the amplifier and the output of the amplifier remainat low voltages. The external device and capacitors see the high voltagesupplied by the voltage gain device. The connector device, the resetdevice and the output stage of the voltage gain device can be lessprecise (e.g., made of high voltage transistors or other componentsdesigned to support the high voltage). Additionally, by selecting thevoltage difference small and the ratio of the unknown capacitance of theexternal device 106 to the capacitance of the second capacitor large,the value the capacitance fo the external device 106 can be determinedwith high precision without generating an large voltage change on theexternal device while the capacitance of the external device isdetermined.

FIGS. 13 and 14 are intended to provide example implementations of thesystems and methods of FIGS. 1-12. FIG. 13 is an example integratedcircuit 1300 that can facilitate applications of the systems and methodsaccording to the embodiments described in the subject disclosure. FIG.14 is an example configuration 1400 of components within an integratedcircuit 1300 that facilitate the applications of the systems and methodsaccording to the embodiments described in the subject disclosure. Itwill be understood that other configurations can be used to facilitateapplications of the systems and methods of FIGS. 1-12 and that FIGS. 13and 14 provide just two example configurations.

The above description of illustrated embodiments, including what isdescribed in the Abstract, is not intended to be exhaustive or to limitthe disclosed embodiments to the precise forms disclosed. While specificembodiments and examples are described herein for illustrative purposes,various modifications are possible that are considered within the scopeof such embodiments and examples, as those skilled in the relevant artcan recognize.

As used herein, the word “example” is used herein to mean serving as anexample, instance, or illustration. For the avoidance of doubt, thesubject matter described herein is not limited by such examples. Inaddition, any aspect or design described herein as an “example” is notnecessarily to be construed as preferred or advantageous over otheraspects or designs, nor is it meant to preclude equivalent structuresand techniques known to those of ordinary skill in the art. Furthermore,to the extent that the terms “includes,” “has,” “contains,” and othersimilar words are used in either the detailed description or the claims,such terms are intended to be inclusive—in a manner similar to the term“comprising” as an open transition word—without precluding anyadditional or other elements.

In this regard, while the described subject matter has been described inconnection with various embodiments and corresponding Figures, whereapplicable, it is to be understood that other similar embodiments can beused or modifications and additions can be made to the describedembodiments for performing the same, similar, alternative, or substitutefunction of the disclosed subject matter without deviating therefrom.Therefore, the disclosed subject matter should not be limited to anysingle embodiment described herein, but rather should be construed inbreadth and scope in accordance with the appended claims.

What is claimed is:
 1. A system, comprising: an amplifier comprising apositive input, a negative input, and an output; a first capacitorconnected to the negative input of the amplifier and to an externaldevice with an unknown capacitance, wherein the first capacitor stores afirst voltage; a second capacitor connected to the output of theamplifier and to the external device, wherein the second capacitorstores the first voltage; a voltage source device that supplies a secondvoltage to the positive input of the amplifier; a reset device thatconnects the output of the amplifier and the negative input of theamplifier; and a detector device that measures a change in the outputvoltage of the amplifier as a function of a change in the second voltagesupplied by the voltage source and function of the unknown capacitanceof the external device, wherein the first voltage is higher than thesecond voltage.
 2. The system of claim 1, wherein the reset device is aswitch, a resistor or an inductor.
 3. The system of claim 1, wherein thereset device, operating together with the amplifier, forces the outputvoltage of the amplifier and the voltage of the negative input of theamplifier to match the voltage of the positive input of the amplifier.4. The system of claim 1, further comprising: a charge generator devicethat facilitates driving the first capacitor, the second capacitor, andthe unknown capacitance of the external device to store the firstvoltage; and a connecting device between the charge generator device andthe external device that provides a first impedance sufficient tofacilitate current flow when the charge generator device drives thefirst capacitor, the second capacitor, and the unknown capacitance ofthe external device to store the first voltage and that provides asecond impedance sufficient to impede current flow when the voltagesource supplies the second voltage to the positive input of theamplifier.
 5. The system of claim 4, wherein the connecting device is aswitch, a resistor or an inductor.
 6. The system of claim 4, wherein thereset device provides a third impedance sufficient to facilitate currentflow when the charge generator device drives the first capacitor, thesecond capacitor, and the unknown capacitance of the external device tostore the first voltage and provides a fourth impedance sufficient toimpede current flow when the voltage source device supplies the secondvoltage to the positive input of the amplifier.
 7. The system of claim1, wherein the voltage source device comprises a pulse generator.
 8. Thesystem of claim 1, wherein the detector device comprises an analog todigital convertor.
 9. The system of claim 1 where the voltage sourcedevice is not connected to the positive input of the amplifier, but to athird capacitor that is connected between the voltage source and thenegative input of the amplifier, the positive input amplifier beingconnected to ground or to a fixed bias voltage.
 10. A method,comprising: storing a first voltage on an external device with anunknown capacitance, on a first capacitor between a negative input of anamplifier and the external device, and on a second capacitor connectedbetween the output of the amplifier and the external device; applying asecond voltage to a positive input of the amplifier; driving a voltageof the output of the amplifier and a voltage of the negative input ofthe amplifier to the second voltage via a reset device; modifying thesecond voltage applied at the positive input of the amplifier; measuringa voltage change of the output of the amplifier that is proportional tothe unknown capacitance and to the voltage change applied at thepositive input of the amplifier, wherein the first voltage is higherthan the second voltage.
 11. The method of claim 10, further comprising:increasing the impedance of a connecting device between a voltage gaindevice and the external device with the unknown capacitance beforemodifying the second voltage applied at the positive input of theamplifier.
 12. The method of claim 10, further comprising: increasingthe impedance of a reset device between the negative input of theamplifier and the output of the amplifier before modifying the secondvoltage applied at the positive input of the amplifier.
 13. The methodof claim 10, wherein the second voltage is about five Volts or less. 14.The method of claim 10, wherein the first voltage is at least abouteight Volts.
 15. The method of claim 10, wherein the applying furthercomprises applying a pulse on the second voltage to the positive inputof the amplifier.
 16. The method of claim 10, wherein the voltage changeat the output of the amplifier corresponds to the voltage change of thepulse of the second voltage multiplied by a ratio of the unknowncapacitance to the second capacitance.
 17. A capacitance measuringcircuit, comprising: an amplifier comprising a positive input, anegative input, and an output; a first capacitor connected to thenegative input of the amplifier and to an external device with anunknown capacitance, wherein the first capacitor stores a first voltage;a second capacitor connected to the output of the amplifier and to theexternal device, wherein the second capacitor stores the first voltage;and a reset device that connects the output of the amplifier and thenegative input of the amplifier and facilitates driving the output ofthe amplifier and the negative input of the amplifier to a secondvoltage supplied by a voltage source device to the positive input of theamplifier, wherein a change in the output voltage of the amplifier as aresult of a change of voltage supplied by the voltage source is afunction of the unknown capacitance of the external device, and whereinthe first voltage is higher than the second voltage.
 18. The capacitancemeasuring circuit of claim 17, further comprising a connection devicebetween a charge generator device and the external device that providesa first impedance sufficient to facilitate current flow when the chargegenerator device drives the first capacitor, the second capacitor, andthe unknown capacitance of the external device to store the firstvoltage and that provides a second impedance sufficient to impedecurrent flow when the voltage source supplies the second voltage to thepositive input of the amplifier.
 19. The capacitance measuring circuitof claim 18, wherein the connection device is a switch, a resistor or aninductor
 20. The capacitance measuring circuit of claim 17, wherein thereset device is a switch, a resistor or an inductor.